Particle therapy is a type of external beam radiotherapy that generates beams of energetic protons, neutrons, or ions used for cancer treatment. Particle therapy works by providing energetic ionizing particles to target tissue (e.g., a tumor). These particles are used to destroy or damage the DNA of tissue cells.
Ion therapy is a type of external beam radiation therapy that is characterized by the use of a beam of ions to irradiate diseased tissue. A chief advantage of ion therapy over other conventional therapies such as X-ray or neutron radiation therapies is that ion radiation has the ability to stop in matter—treatment dosages are applied as a sequence of proton beams with several energies three-dimensionally. The dose deposition of each monoenergetic, thin (“pencil”) beam in a medium is characterized by a sharp increase in dose deposition (Single Bragg Peak) directly before the end of the beam depth, thereby limiting the inadvertent exposure of non-target cells to potentially harmful radiation.
The pencil beam scanning technique allows the deflection of monoenergetic beams to prescribed voxels (in transversal direction/x- and y-coordinates for associated beam depths) in medium—the so called spot scanning technique (e.g., a “raster scan” of applications). Prescribed spot positions for a scanned ion beam delivery are typically arranged on a fixed (raster) pattern for each energy and therefore deliverable on a fixed scanning path within an energy layer (for example on a meander like path). By superposition of several ion beams of different energies, a Bragg peak can be spread out to cover target volumes by a uniform, prescribed dose. This enables ion therapy treatments to more precisely localize the radiation dosage relative to other types of external beam radiotherapy. During ion therapy treatment, a particle accelerator such as a cyclotron or synchrotron is used to generate a beam of ions from, for example, an internal ion source located in the center of the cyclotron. The ions in the beam are accelerated (via a generated electric field), and the beam of accelerated ions is subsequently “extracted” and magnetically directed through a series of interconnecting tubes (called a beamline), often through multiple chambers, rooms, or even floors of a building, before finally being applied through an end section of beam line (called Nozzle) to a target volume in a treatment room.
As the volumes (e.g., organs, or regions of a body) targeted for radiation therapy are often below the surface of the skin and/or extend in three dimensions, and since ion therapy—like all radiation therapies—can be harmful to intervening tissue located in a subject between the target area and the beam emitter, the precise calculation and application of correct dosage amounts and positions are critical to avoid exposing non target areas to the radiation beyond what is necessary. However, the effective ion range is variable based on a number of uncertainties, such as positional discrepancies and motion, and understanding of the sources and magnitude of these uncertainties is key for producing treatment plans which are robust and can withstand these uncertainties. Furthermore, for intensity-modulated particle therapy (IMPT), steep dose gradients are often used at the target border and field edges to enhance dose conformity. This increases the complexity of fluence maps and decreases robustness to uncertainties.
To address these issues, adaptive therapy techniques have been proposed that incorporate such uncertainties directly into the optimization algorithm. According to some techniques, robustness may be included in a multi-criteria optimization framework, allowing a multi-objective optimization function to balance robustness and conformity. For mitigating the effects of motion specifically, rescanning (“repainting”) techniques have been developed to deliver the prescribed dose distribution to each layer of the target volume. However, the repainting techniques currently employed lead to an under-dose and/or over-dose pattern based on motion parameters (e.g., initial phase, period, amplitude) and the speed and/or direction of the scanning, leading to artifacts caused by a predominant scanning direction. What is needed is an approach to repainting that mitigates the under-dose and/or over-dose pattern inherent in existing repainting techniques while achieving a relatively uniform dose distribution.